They appear to work just fine but their dimensions are slightly smaller than the brands I previously used. We have an intake that's in the ceiling, when the air turns on it gets sucked up, then when the air turns off it drops down again. While the movement is minimal, we do hear it so I'll have to get up there and find something (weather stripping maybe?) to keep it snug. Unless the do a poor job in the spring, I will continue to purchase these.